Bomb sight



d" 22 m4 H. c. VAN AUKEN 1:1- AL 2,409,648

BOMB SIGHT f Filed Jan. 25, 1941 3 sheets-sheet s Patented Get. 22, 1946 angers UNI'rED STATES PATENT oFFlcE BOMB SIGHT Howard C. Van Auken, Bloomfield, and Gerald N. Hanson, Allendale, N. J., assignors to Sperry Gyroscope Company, Inc., Brooklyn, N. Y., a corporation of New York Application `lanuary 25, 1941, Serial No. 375,900

8 Claims.

This invention relates to bomb sights for aircraft which are designed to direct the course of the craft so that its ground track, except for offset, would pass through the target in a straight line and which determine the exact point at which the bombs should be released to strike the target. This mechanism also preferably computes and sets in automatically the amount of offset necessary to compensate for side drift due to side winds.

More particularly, our invention constitutes an improvement in cr further development of the type of bomb sight disclosed in the prior patent to Howard C. Van Auken, one of the joint patentees, and Earl W. Chafee, No. 2,371,606, titled Bomb sights. More particularly, our invention constitutes an improvement in the optical systems of bomb sights in general, and the system disclosed in the aforesaid application in particular, wherein the offset angle is set into the optics in an improved manner by adjusting a prism or reflector or other line of sight deflector mounted on an unstabilized part, about a normally vertical axis.

A further improvement consists in the provision of a means for shifting the altitude scale employed in the mechanism so that the sight may not only be used for normally high altitude bombing, say at 4000 feet and above, but so that it may also be used for low altitude bombing, i. e., under 4000 feet.

Referring to the drawings, illustrating the preferred form of our invention,

Fig. 1 is a vertical section through our improved form of stabilized sight.

Fig. 2 is a diagram illustrating the principles involved in the bomb sight in the presence of side wind.

Figs. 3A and 3B together constitute a diagrammatic layout of the computing mechanism of the sight, Fig. 3A being the left hand portion of the diagram and Fig. 3B the right hand portion thereof.

Referring first to Fig. l, we prefer to employ an artificial horizon, such as some form of gyroscope I', to stabilize the line of sight against rolling and pitching. As shown, the gyro rotor casing I is universally mounted within a supporting, universally mounted framework 2 by means of gimbal ring 3 pivoted on major axis Al-Ll within framework 2 and pivotally supporting the gyro casing, in turn, on minor axis 5-5. The gyroscope is preferably mounted in neutral equilibrium, but is equipped with a suitable power actuated erection device, which may be of the standard differential air port type employing a 2 plurality of pendulous shutters 6 cooperating in conjunction with air ports 6', as well understood in the art. The framework 2 is shown as mounted for rotation about a normally vertical axis within the outer fixed frame 9 by means of roller supports I0 on which a circular inclined trackway I I, secured to frame 2, rests.

The framework 2 is normally maintained xed in azimuth from al directional gyroscope I2 (Fig. 3B), as hereinafter described, as by means of a shaft I3 carrying a pinion I4 meshing with an annular gear I5 on the bottom of frame 2, so that the entire gyroscope and its connected optics is maintained xed in azimuth. Guide rollers I I may also be utilized in addition to rollers I0.

On the top of the gyro casing I is mounted the reticle or cross hairs I0, which therefore is stabilized about all three axes. While stabilization of the reticle has been found sufficient for some purposes, we prefer to also stabilize against rolling at least the main target following reflecting prism or mirror I'I and one of the intermediate prisms (I8). To this end, both of said prisms I1 and I3 are shown as mounted on forwardly extending arms I9 from gimbal ring 3, said arms passing around the forward gimbal pivot 4, as shown in Fig. 3B. Said prisms therefore are stabilized against rolling and in azimuth, although not stabilized against pitching in the form sho-wn. Prism I'I is shown as pivoted on transverse axis 32 in said arms I9 so that it may be tilted to follow the target. By so stabilizing the reflecting prism, the apparent yaw of the line of sight caused by false yaw due to rolling of the craft is eliminated.

From intermediate prism I8, the line of sight passes vertically upwardly into the objective lens system 20 which focuses the image of the ground in the plane of the reticle I6, which is located above but laterally displaced from the lens. Preferably, the reticle is directly over the center of the gyroscope and the line of sight from thel objective lens is displaced laterally -to the center of the gyroscope and thence upwardly through reflecting prisms or mirrors 2| and 22. The objective lens and prisms-are mounted on the rotatable frame 2, but are not shown stabilized from the gyroscope I, as this is unnecessary, said parts being, mounted on a bracket 321 secured to frame 2. Finally, the image projected on the reticle is viewed from a telescopic eye piece 23.

For causing the prism I'l to follow the target, we have shown a bell crank lever 25 pivoted at 26 on the frame 321 supporting the objective lens and having at its lower end a transversely posiu tioned channel member 28 engaging a knob 29 projecting upwardly from the back of the metal mounting of the prism Il'. Therefore, any movement of the bell crank lever in the plane of the paper in Fig. 1, that is, fore and aft of the craft, will rock the prism to follow the target, but rolling of the craft will not affect the prism, since the prism is stabilized from. the gyroscope and the knob 29 will merely slide back and forth in the channel 28. The bell crank lever is rocked by the engagement of its upper end 33 with a member 3| moved by the computing mechanism of the sight, the lever being shown as having a knob on the end thereof to be engaged by the vmember One of the improvements over the prior application consists in the mounting of the prism 2|.

According to our invention, we perfer to 'adjustably mount the prism so as to incorporate in the sight the offset angle F (Fig. 2). For this purpose, the prism 2| is rotatably mounted about a normally vertical axis Yin the fixed framework, the back |21 of the prism being shown as secured to a shaft 21' journaled in anti-friction bearings 2 in bracket 23. Adjustment of the prism about the vertical axis is automatically accomplished by means of an arm M9 secured to the back of frame |21' and projecting laterally behind the objective lens 2li `and telescope 23. The end of said arm |139 is shown as carrying a roller |49 which normally is yieldingly held against a semicircular ring S8 secured to the bottom of an arm |41 extending downwardly from a gimbal |46 journaled on transverse shaft i635 (Fig. 3B). Said .gimbal has va long laterally extending arm |46, the end of which is moved up and down by a'pin '|455 on a lever IM, as hereinafter described to impart the proper function of the offset angle to prism 2|.

The Vcomputing mechanism is principally for the purpose of determining the point R. at which to release the bomb to hit the target T at which the sight is'directed (Fig. 2). The horizontal distance from the target to the projection of this lpoint on the ground is known as the range (PT), and the angle that the line of sight makes at this time istheY range angle (0). It is also for the pur- 'pose of determining the true ground Acourse of the craft (OVl) and for directing the pilot so the bombs trajectory (curve RT) Will intersect Vthe target T. For turning the prism |1'about its pivotal axis 32 to maintain the same on the target, we have shown the knob engaging member 3l as moved upm-and down from a spring 3|' and a rod 33, which rod, in turn,`is moved by the rotation of the sight angle cam 3 4. Said cam is shown as mounted on a shaft 35 ywhich also moves the moving contact lllon the bomb release mechanism, said shaft being shown as having a pinion 31 thereon meshing with a vertical rack 38 carrying the contact |33. Said shaft 35 is shown as driven by means of a Worm 39, a worm wheel and a slip clutch 4| from shaft l2 which, in turn, is driven through bevel gears 4| from shaft 43, which in turn is driven through gears 44 from one side of the differential (l5.

Initial setting ofthe prism l1 on the target may be accomplished by'a knob 235, to which a sight angle scale 236 may be secured. Said knob `is geareddirectly through bevel gears 231 to shaft 35 to turn cam 34. Another arm of said diiferential is'shown as driven from gear 48, shown asdriven from 'a"p`inion"ll`9'(Fig. A3A), secured Vbracket 335 engages. `as pvoted, on said bracket 335 and as hav- "a long pin'301 freely extends.

trail V1?.

angle' 0.

4 to the driven member or cylinder 50 of the ground speed variable speed drive mechanism (GSVSD) Since the greater part of the mechanism of the present invention, pertaining to the obtaining of the various factors in the sight, is the same as completely described in the aforesaid previous joint application Serial No. 128,034, it is thought unnecessary to burden the present application with a complete description of the same, but to enable the reader to understand the mechanism, applicants have placed the same reference characters and legends on the corresponding parts in th'e present application as are used in the aforesaid prior application. For instance, the four three dimensional cams |015, ||2, |21 and |29 employed in the mechanism may be identical with the cams employed in the prior application. These cams may be briefly designated as the whole range cam |95, the time of fall cam 2, the trail cam |21, and the square of the time of fall cam |29.

There are also employed a plurality of power supplying variable speed drives of special construction all of which are preferably primarily Vactuated from the common constant speed motor `Said drives may be briefly identied as the ground rspeed variable speed drive 56, 52, 5,4 I(GSVS'D), the altitude variable speed drive 66, 51, '63 (HVSD), the vertical velocity variable:

speed vdrive 13, 19 (VVVSD), and the azimuth variable speed drive |88, |92 (AVSD). The functions of these drives are also substantially identical with similar parts described in the aforesaid :prior application. The various settings for ve- .a locity of glide and ballistic coefficient, initial altitude, trail angle, and barometric or altitude settingare also substantially the same.

Asjbeforel stated, however, the mechanism by which the offset angle is introduced in my present invention `is diierent from the prior application. AReferring to Fig. 2, itmay be shown that the offset angle F is proportional to the offset OP multiplied by the cosine of the range angle 0 or, in other words,

FaOP cos 0 (l) the sine Aof the drift angle (D), which is the angle between'the heading (RS) and the actual course (RC) of the aircraft, or

OP=V1T sin D Therefore equation (l) may bel written FaV1'T sin `D cos 0 (2) From the foregoing description in connection with the prior application, it is apparent that the angular position of the cam 34 or, in other words, of 'shaft 351m which'it is mounted, is proportional vto tan 0, and therefore the position 0f this vshaft may beutilized to give the function cosine 0 in the above equation'b'y means of a helixmrl cut in a cylinder 3%2 on shaft 35, in Ywhich a vpin 363 on slidable U-'shaped A lever 30'!! is 'shown ing fa slot '33t vin its outer end through which m Y Said pin is secured to the trail lift pin |||l of the trail cam |21 -so that said pin is moved in-accordance with the The lever (30d also has a pin 338 eX- tending laterally'through'a slot in a Vlever 3DS secured to the shaft |35'. VTherefore shaft |35 is positioned in accordance `with a function of the trail (V1T) and the Vcosine of the range The shaft |35 angularly positions the angle bar |39 which the pin |46 of the long member |4| adjustably engages. Said lever is shown as pivoted at IAS on a sliding rack bar I8 which, in turn, is laterally positioned in accordance with the drift angle D by setting knob 3|@ so that the drift angle pointer |80 matches the drift angle as observed on the drift angle scale |80. This movement moves the rack bar to the right or left in Fig. 3B and thereby shifts the position of the pin ld on the inclined surface |39 to introduce the sine function of the vdrift angle. The other end of the lever Ml is provided with a pin |45 engaging the outer end of the long lever |46, hereinbefore described, to rotate the Prism 2| through the arm |69 to thereby set in the aforesaid offset angle.

As hereinbefore stated, our sight is primarily designed lfor operation above about 4000 feet. In order that the sight may be used for lower altitudes, we have introduced a change speed mechanism interposed between the constant speed motor 53 and atleast the altitude variable speed drive 56 (I-IVSD) and the ground speed drive 50 (GSi/'SDL Said mechanism is shown as involving change speed gearing 320, including a shiftable clutch S25 adapted to be thrown by a handle 322 into normal or high speed. In its normal position, the handle is positioned to close contact 323. For the high altitude position, all parts function as above described and the bomb release contacts |99 are in circuit withthe bomb release mechanism 22S. When the change speed mechanism is thrown to the right, however, the speed discs of the variable speed drives are driven at, say, four times the original velocity and contacts 325 are made to throw lin auxiliary bomb release contacts 340.

When using the sight at low altitude, the sight proper can only be used to give on ground speed dial G. S. 58, an indication which at a predetermined altitude (say 1000 feet) shows true ground speed. It will also show ground speed at any altitude below 4000 when multiplied by the ratio of the actual altitude to 1000 (h/H'). A chart is then consulted, from which approximate data is obtained to set the auxiliary range angle scale 23S by knob 335, thereby setting the position of the contact 340. While the sight, therefore, is not fully automatic below 4000 feet, it can be used to give data from which the bomb release point may be readily obtained and it is fully automatic for 4000 feet up to the top limit for which it is designed.

It is also interesting to note that the ground speed scale may be made to read correctly without interpolation, for low altitudes if the ball carriage 68 on the altitude variable speed drive (HVSD) be moved through four times the distance it is moved for a given change in h/H, when operating in the high altitude range.

It will of course be understood that the ratio and altitude figures given above are merely by way of example and that the altitude limits may be Varied greatly to meet the current requirements.

While as stated above, most of the mechanism in the present application follows closely that shown in the aforesaid prior application of Chafee and Van Auken, the stabilization or fixing of the optics in azimuth from the directional gyroscope i2 departs somewhat from the disclosure in the aforesaid prior application. In the present application, the pick-olf from the directional gyroscope l2 is of the electro-inductive type of the type shown, for instance, in prior patent to Moseley, Cooke and Frische No. 27,139,558, for Follow-up system for gyro compasses, dated December 6, 1938, instead of being of the differential airflow type. A soft iron armature 350 is secured to the vertical ring |58 of the directional gyro l2 so that it is moved across the outer legs of a three-fingered transformer |60 and |60 to control through a suitable electronic circuit (not shown), a reversible follow-up motor 53', said motor driving through suitable gearing dilo and 40|, a follow-back to the plate |6| carrying the transformer and also driving through shaft |62, worm 202, differential |18 and shaft |3, the pinion ifi which rotates the base I5 on which the entire stabilizing gyroscope and optical system, except the telescope, is mounted.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described our invention, what we claim and desire to secure by Letters Patent is:

l. In a bombsight for aircraft, in combination with a gyro vertical, a sighting reticle mounted thereon and stabilized thereby about both foreand-aft and transverse horizontal axes, a reflector for following the target stabilized about said fore-and-aft axes and mounted for turning about a transverse axis, and adapted to direct the line of sight horizontally along said fore-and-aft axis, a second reflector also stabilized about said axis for receiving said line of sight and directing it vertically, a third reector for receiving the line of sight as reflected from said last-named reflector and directing the same horizontally toward the reticle, and means adapted to produce independent rotation of said last-named reflector relative to said other reflectors about a normally vertical axis to introduce the offset angle.

2. In a bombsight for aircraft, an observing eye piece, an artificial horizon such-as a gyro-vertical, a reticle stabilized therefrom about a normally fore and aft and an athwartship axis, a pivoted reflector for reflecting an image of the target on said reticle and thence into said eye piece, said reflector being stabilized by said artificial horizon about said fore and aft axis, a second unstabilized reflector in the line of Sight between said rst refiector and said eye piece, said second reflector being mounted for rotation relative to said first reflector about a normally vertical axis, and means for adjusting said last reflector about said vertical axis in accordance with an offset angle.

3. A stabilized bombsight for aircraft including a gyro vertical having a vertical axis stabilized about both horizontal axes and also in azimuth, a reticle mounted thereon and extending perpendicular to said axis, and means for focusing an image of the target vertically upward on said reticle including a pair of 45 reflectors mounted independently of said gyroscope for displacing the vertical line of sight to one side of the gyroscope, a third 45 reflector for directing said line of sight along the heading of the craft, a fourth reflector for deecting the line of sight on the target, and means for tilting said last named reflector about a lateral axis for following the target, said last two reflectors being stabilized in azimuth and against rolling by said gyroscope.

4. A stabilized bombsight for aircraft including va gyro vertical having a vertical axis stabilized about both horizontal axes and Yalso in azimuth,

lecting line of sight on the target, and means forA tilting said last named reflector about a lateral Yaxis for following the target, means for maintaining an azimuth reference line, and means for stabilizing said last two reflectors in azimuth therefrom and against rolling by said gyroscope.

5. In a bombsight for use at both lowand high altitudes, rotatably mounted sighting means for following a target, Variable speed driving means for rotating said sighting means according to ground speed, power means for driving a member of said variable speed drive at a substantially constant speed, a control device having low and high altitude positions, means responsive to the low altitude position of said control device for causing said power means to drive said member at a high constant speed, means responsive to the high altitude position of said control device for causing said power means to drive said member at a lower constant speed, a low altitude bomb release Contact, a high altitude bomb release contact, said contacts being arranged according to changes in scale factors due to different speeds of said member, and means operated by said control device for shifting control of the bomb release mechanism between said contacts according to the position of said device.

6. In a bombsight for aircraft, in combination, a gyro, a sighting reticle supported for stabilization about two axes by said gyro, a sighting deflector mounted for stabilization by saidV gyro about one of said axes and pivotally supported for rotation independently ofvsaid gyro about a transverse axis, and a separate unstabilized defiector arranged in an optical system between said sighting deector and said reticle to provide a stabilized line of sight movable in a stabilized plane to follow a target by turning said sighting deflector about said transverse axis, said unstabi- 'lized delector being pivotally supported to turn relative to said sighting deilector and said reticle for laterally offsetting said line of sight as well as its plane of movement without disturbing the stabilization thereof.

7. in a bombsight for aircraft, in combination, a gyro, a sighting retcle supported for stabilization about two axes by said gyro, a sighting deilector mounted for stabilization by said gyro about one of vsaid. axes and pivotally supported for rotation independently of said gyro about a transverse axis, an unstabilized eye piece mounted independently of said gyro, a separate unstabilized vdeiiector pivotally supported between said sighting defiector and said eye piece for move'- ment independently thereof, said deectors being so arranged with respect to said stabilized reticle to denne a stabilized line of sight from said eye piece, means for turning said sighting deflector about said transverse axis to move said line of sight in a stabilized plane to follow a target, and means for turning said unstabilized deflector about its pivotal axis according to the offset angle to angularly displace said stabilized plane and said line of sight to compensate for the effect of a cross wind.

In a bombsight for aircraft including an optical system dening a line of sight, apparatus for correcting for the 'oiTset angle between the line of pensate for the eiect of a cross wind of the trajectory'of the bomb, a member displaceable according tc the drift angle between the line of flight and the heading of the craft, and a multiplier mechanism operated jointly by said last named member and said output member for moving said deector to oiset the line of sight according to the computed offset angle.

HOWARD C. VAN AUKEN. GERALD N. HANSON. 

